Low-temperature joining of boron carbide (B 4 C) ceramics using an Al sheet was investigated in the temperature range of 600 1200°C for 2 h in vacuum (10 ¹2 10 ¹4 Pa). Successful joining and high bending strength close to that of the B 4 C base were achieved in the samples joined at 7001100°C. Different techniques including scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and transmission electron microscopy (TEM) were used to characterize the high-strength B 4 C joints. SEM observations suggested the dense interlayer and the crack-free interface as well as the penetration of Al into the surface microcracks of B 4 C base. Further TEM examinations revealed that B 4 C and Al joined directly. EPMA analysis demonstrated the existence of several reaction products within interlayer, including AlB 2 and Al 3 BC, which resulted in the development of high-strength composite interlayer.

Impact damage of laminated B 4 C ceramic samples was investigated using four types of aluminum sheets -without holes and with 25 4-, 8-, and 25-mm-diameter holes -at joining ratios of 100, 94, 76, and 45%. Four 1-mm-thick B 4 C ceramics plates were laminated using three aluminum sheets of the same type and joined at 700°C in vacuum. In impact damage tests using spherical SUJ-2 projectile with a diameter of 4 mm with a velocity of approximately 300 ms À1 , bulk B 4 C showed a large conical crack and significant fractures; the conical crack in the laminated samples was smaller than that of the bulk B 4 C. However, the conical cracks of the laminated B 4 C with the joining ratio 45 to 96% were of the same size, irrespective of the joining ratios. The total load and induced pressure area on the rear side of laminated samples were smaller than that observed for bulk B 4 C, and total load and induced pressure area were similar for laminated samples with high and low joining ratios. The maximum pressure on the rear face of laminated B 4 C samples was higher than that observed for bulk B 4 C and increased with decreasing joining ratio of laminate interlayer.

Ceramics will be widely used for enhancing the efficiency of power generating systems, particularly gas turbines. However, ceramics used in these systems suffer damage owing to impact by foreign objects. In this study, various ceramic plates are impacted by a spherical projectile with an impact velocity of 320 m/s. The volume of the cone cracks formed on the plates decreases with an increase in the fracture toughness of the ceramic material. No cone cracks are formed on the zirconia (3Y-TZP) plate because crack formation is prevented by stress-induced phase transformation outside the impacted region. The volume of the cone crack is higher and the energy consumed by surface formation is smaller in transgranular-fractured ceramics than in intergranular-fractured ones. The fracture process can be controlled by controlling the characteristics of the grain boundaries, as well as by stress-induced phase transformation.

The influence of the joining time and temperature on the flexural strength of B 4 C ceramics joined using an Al sheet was investigated. The B 4 C ceramics were joined over a temperature range 6001400°C for 272 h in vacuum (10 ¹2 10 ¹4 Pa) and in an Ar atmosphere. A joining interlayer with a dense structure was found in the B 4 C joint formed at 1000°C after 2 h in vacuum, and mainly Al was present in this joining interlayer. On the other hand, some voids existed in the joining interlayer in the B 4 C joint formed after 72 h. In addition, Al was not present in this interlayer owing to its reaction with B 4 C as well as the evaporation of Al. Four-point bending tests of the B 4 C joints formed at 1000°C in vacuum for periods ranging from 2 to 72 h were performed at room temperature. The average four-point bending strengths of the B 4 C joints formed after 2 h at 7001100°C were close to that of the B 4 C base material, and the B 4 C ceramics were considered to have successfully bonded. However, the joint strength decreased with an increase in the joining time, and the B 4 C ceramics did not bond at temperatures over 1200°C in vacuum. On the other hand, the B 4 C ceramics did bond at 12001400°C in Ar.